A light guide plate is a significant component of a side incident backlight module and used to transform a linear light source to a planar light source.
FIG. 1 is a partial cross-sectional view of an existing backlight module, and the backlight module mainly comprises: a reflective film 11, a light guide plate 12, a diffusing film 13, a lens film 14, a lamp strip 15 and a back plate 16; the LED lamp strip 15 comprises a printed circuit board (PCB) 151 and a plurality of LED (Light-Emitting Diode) lamps 152 welded on the PCB 151; a light emitting surface of the LED lamp 152 is opposite to a light incident surface 121 of a side portion of the light guide plate 12, so as to allow the light emitted from the LED lamp 152 to enter the light guide plate 12 from the light incident surface 121, and the light will emit from the light emitting surface 122 of the top portion of the light guide plate 12 after refracted or reflected in the light guide plate 12. The diffusing film 13 and the lens film 14 are used to converge the light emitted from the light emitting surface to an intended range of viewing angle.
In assembling the above backlight module, as illustrated by FIG. 1, it is needed to bond the LED lamp strip 15 onto the back plate 16 via a lamp strip fixing tape 17 at first, then lock the light guide plate 12 to a bayonet of the back plate 16, so as to enable the light emitting surface of the LED lamp 152 to be opposite to light incident surface 121 of the side portion of the light guide plate 12. Because the installation of the LED lamp strip 15 and the installation of the light guide plate 12 are separated, it is hard to guarantee the light emitting surface of the LED lamp 152 be totally right-opposite to the light incident surface of the light guide plate 12 (i.e., as illustrated by the imaginary line in FIG. 1, the center line 153 of the light emitting surface of the LED lamp 152 coincide the center line 123 of the light incident surface of the light guide plate 12). When the light emitting surface of the LED lamp 152 and the light incident surface of the light guide plate 12 can not be totally right-opposite, it is easy for hot dot phenomenon to appear on the light emitting surface 121 of the light guide plate 12, as illustrated by FIG. 2, the solid lines with arrows represent the transmitting routes of the light emitted from the LED lamp 152.